Method and device for predicting the flocculation threshold of asphaltenes contained in hydrocarbon mixtures

Abstract

Method and device for predicting the flocculation threshold of asphaltenes contained in hydrocarbon mixtures.The method comprises the following stages:determining the refraction index (nA) of several asphaltenes used as reference asphaltenes;determining experimentally, for predetermined thermodynamic conditions, the variation of solubility index (delta) in connection with the refraction index of hydrocarbon constituents including light hydrocarbons and reference asphaltenes;deducing therefrom a correlation relation modelling this variation of solubility index (delta).These preliminary operations being performed,refraction index (nA) of the asphaltenes of the hydrocarbon mixture is determined under the same thermodynamic conditions and by reference to said correlation relation, solubility index (delta) of the asphaltenes of said mixture is deduced therefrom; andfrom the solubility index of the asphaltenes of said mixture and from a thermodynamic equilibrium model, the flocculation threshold thereof is directly predicted.Applications: fast laboratory determination of asphaltene flocculation risks likely to hinder production and transport of crudes so as to quickly implement solutions intended to prevent them.

What is claimed is:  
     
       1. A method for predicting the flocculation threshold of asphaltenes contained in a hydrocarbon mixture, characterized in that the following stages are carried out: 
       determining the refraction index (n A ) of several asphaltenes used as reference asphaltenes;  
       determining experimentally, for predetermined thermodynamic conditions, the variation of solubility index (δ) in connection with the refraction index of hydrocarbon constituents including light hydrocarbons and reference asphaltenes;  
       deducing therefrom a correlation relation modelling this variation of solubility index (δ).  
       determining refraction index (n A ) of the asphaltenes of the hydrocarbon mixture under the same thermodynamic conditions and by reference to said correlation relation, deducing solubility index (δ) of the asphaltenes of said mixture therefrom; and  
       predicting directly the flocculation threshold from the solubility index of the asphaltenes of said mixture and from a thermodynamic equilibrium model.  
     
     
       2. A method as claimed in  claim 1 , characterized in that the variation of refraction index (n A ) is determined by extrapolation from measured refraction index values obtained for several solutions of relatively low concentration of these asphaltenes in solvents. 
     
     
       3. A device for predicting the flocculation threshold of asphaltenes contained in a given hydrocarbon mixture, characterized in that it comprises a refractometer ( 2 ) and a system ( 1 ,  3 ) suited to experimentally determine, under predetermined thermodynamic conditions, the refraction index (n A ) of asphaltenes, to determine the variations of solubility index (δ) in connection with variations of the refraction index of known hydrocarbon constituents including light hydrocarbons and of several known reference asphaltenes, to deduce therefrom a correlation relation modelling these variations of solubility index (δ), and to apply this correlation relation to a thermodynamic equilibrium model to directly predict the flocculation threshold of the asphaltenes contained in said hydrocarbon mixture. 
     
     
       4. A device as claimed in  claim 3 , characterized in that the system comprises a programmed computer ( 3 ). 
     
     
       5. A device as claimed in  claim 3 , characterized in that the system comprises a programmed computer ( 3 ) and a device ( 1 ) for bringing asphaltenes into solution in a solvent at variable concentrations.